MELOLONTHINAE Leach in Samouelle, 1819
Includes diurnal and nocturnal species, most of which become locally abundant during short seasons in the spring or summer.
The limits of this group are far from settled and various other groups are often included as tribes e.g. Euchrinae Hope, 1840 or Pachypodinae Erichson, 1840, but generally it will be found to include between 20 and 30 tribes and around 12000 species in about 800 genera. Because the limits and the definition of tribes and subfamilies have not been used consistently, the whole tribal classification remains confused and is in need of revision, this is going to be a major undertaking as many older descriptions of genera and species are inadequate and type material will need to be reassessed, for these reasons the following discussion will be centred around the northern Temperate fauna which is generally much better understood. Even individual genera may be very difficult to assess because many species tend to get lumped into large genera regardless of their phylogenetic or taxonomic affinities, this is probably true of many tropical areas with very diverse faunas which have been largely ignored. Having said that we have a recent (2018) checklist where the Melolonthinae is included as a subfamily of the Scarabaeidae Latreille, 1802, which is a historically stable situation with which we are all familiar, but the Fauna Europaea website (which attempts to deal with the entire European fauna) presents the group as a family, Melolonthidae, and even some of our familiar UK chafers such as Serica brunnea (Linnaeus, 1758) are assigned to distinct subfamilies, in this case the Sericinae Kirby, 1837. In order to present our UK fauna in a familiar context we will adhere mostly to our recent checklist. The greatest diversity by far is in tropical and subtropical regions but temperate regions tend to have relatively diverse faunas e.g., the New World fauna includes about 2700 described species of 125 genera whereas that of the Nearctic region includes more than 600 species of 30 genera. The European fauna includes 33 genera and about 300 species, most of which occur in southern regions and many of which are of restricted distributions, but of the many widespread species 8 extend to the UK (see below). Worldwide many smaller areas and islands are rich in endemic species and this is a feature of many of the tribes e.g. of the 50 or so species and 10 genera known from Sri Lanka almost 90% are endemic, and in general the faunas of the major tropical regions tend to be distinctive.
The following description applies to the group as a whole but refers mostly to the Holarctic fauna with only occasional references to the enormous morphological diversity seen in tropical species. Adults are readily recognized as chafers but there are other superficially similar groups of chafers e.g. Glaphyridae and so unfamiliar material will need to be treated carefully. Adults range from 3mm to about 60mm and are broadly-oval and convex, most are brown to reddish-brown or black, sometimes with a metallic green, blue or red reflection, and most are conspicuously pubescent or scaled, this vestiture may be evenly distributed or arranged in patches or patterns. The head is usually unmodified, although may display sexual dimorphism, with well-developed mandibles and a transverse to conical labrum located below the clypeus or on the clypeal margin, the antennae are placed laterally in front of large and convex eyes, the insertions being hidden from above under the lateral clypeal margin. Antennae short and 7 to 10 segmented, the basal segment enlarged and the distal segments variously lamellate and forming a 3 to 7 segmented club which can be folded or widely expanded like a fan, this is usually glabrous or with only a few scattered setae and almost always sexually dimorphic, being often greatly enlarged in males. Thorax transverse and unarmed; simply convex or variously explanate, much wider than the head and usually as broad as the elytral base. Scutellum exposed and usually large. Ventral surface convex and usually pubescent, the mesepimeron covered by the base of the elytra. Abdomen with at most 7 pairs of spiracles; one pair exposed beneath the elytral margin and the posterior spiracles placed in sternites, tergites or pleural membranes, with 5 or 6 variously fused sternites, the sutures visible at least laterally (rarely completely extinguished), the sixth sternite sometimes partially or completely retracted into the fifth, and the pygidium well-developed, often enlarged and exposed beyond the elytral apex. Elytra convex and usually with a few variously-developed longitudinal ridges, shoulders well-developed and lateral margins sinuate to straight but not indented posterior to the humerus, usually explanate and with narrow epipleura. Hind wings well-developed. Legs long and robust with transverse coxae and relatively large trochanters obliquely connected to broad femora. Front tibiae fossorial, with several large external teeth towards the apex, middle and hind tibiae usually with several transverse ridges or pairs of spines along the outer margin, middle tibiae usually with a pair of short apical spurs, hind tibiae with 1 or 2 long spurs either separated by the basal tarsomere or adjacent. Claws paired or (in Hoplia) single and cleft, toothed, serrate or pectinate. Sexual dimorphism is often obvious but not developed to the extent seen in many Cetoniinae Leach, 1815; males usually have the abdomen less convex, the tarsi longer and the antennal club more developed, in some groups they lack front and hind tibial spurs or have specialized front claws.
The pale C-shaped subterranean larvae are familiar horticultural pests in many gardens; they are typically white or creamy with a darker, well-sclerotized head, a lateral row of dark spiracles and prominent legs. They will often have the apical half or third of the body extensively darkened from digested food. They may be distinguished from other subterranean larvae as follows: Head with large and prominent mandibles that usually lack a stridulatory area and have a distal blade-like inner margin separated from the proximal margin by a scissorial notch, maxillary galea and lacinia fused basally but separate distally, lacinia with a longitudinal row of 3 unci, maxillary stridulatory area without an anterior process. Antennae 4-segmented and often long, the terminal segment with an elliptical sensory spot. Thoracic segments usually not obviously different from the abdominal segments, each with a well-developed and 4-segmented leg, each claw bearing 2 setae. Anal opening angled or Y-shaped, the lower anal margin usually cleft or with grooves.
In northern temperate regions most species are univoltine, although at higher latitudes two or three years of larval development is common, with adults occurring over a well-defined and often brief season during late spring and early summer (adults are variously called May-bugs or summer chafers). Adults may be diurnal, crepuscular or (the majority) nocturnal, they fly well, often swarm around host plants and many come to light traps in numbers. They generally feed on leaves or developing leaf-buds of a very wide range of trees and shrubs although some do not feed at all, mating occurs on or around the host plants and females oviposit in the ground. The subterranean larvae feed on roots, rhizomes and tubers, mostly of grasses and herbaceous plants but also on trees and shrubs, they may develop over several years and in many species regular or sporadic massive populations of adults occur. There are three larval instars and generations overlap so that larvae in several stages of development may occur in the same area of ground. Large populations of larvae may be damaging to turf or agricultural crops while adults may completely defoliate trees while feeding nocturnally and species of some genera e.g. Melolontha Fabricius, 1775, Amphimallon Latreille, 1825, Polyphylla Harris, 1841 and Serica Macleay, 1819 (to quote a few familiar UK groups but there are many others) are occasionally very serious economic pests of a wide range of crops and amenity turfs. Many species prefer light sandy or chalky soils that are not prone to water-logging and in which the larvae can move easily from plant to plant consuming roots; some are localized by soil type, but many common species, given the opportunity, will infest any reasonably dry soil and well-maintained turfs such as golf greens and tees of bowling-greens often seem to be particularly attractive.
Lepidiota stigma Fabricius, 1798
Overwintering larvae usually move deeper into the soil and ascend in the spring to resume feeding, pupation occurs in a subterranean cell a few weeks before the adults eclose and adults often emerge from the soil synchronously so that damage to surrounding trees and shrubs may occur suddenly and be severe. Adults of diurnal species tend to inhabit flowers and feed on pollen and some groups e.g. the cosmopolitan Hopliini Latreille, 1829, are important pollinators in some regions. Unusually, some Australian species occur in termite nests. Among the many tropical pest chafers some of the most damaging are species of the widespread genus Lepidiota Kirby, 1828, most notoriously L. stigma Fabricius, 1798, a destructive pest of sugar cane, corn, sorghum and a wide range of fruits, and the southeast Asian and Australasian genus Dermolepida Arrow, 1941, especially D. albohirtum (Waterhouse, 1875) a destructive Australian native which attacks sugar cane.
All UK species are very typical of the subfamily and represent much larger genera. Hoplia Illiger, 1803 includes about 300 species worldwide; about 170 occur in the Palaearctic region and 40 are European. Melolontha includes at least 60 species and specimens of many more await description, the genus is Palaearctic with several species extending south into the Oriental region, the greatest diversity is in eastern Asia and especially China, 6 species occur in Europe. Polyphylla is a Holarctic genus extending south into Central America, Africa and Southeast Asia; more than 80 species are described of which 34 occur in the Palaearctic region and 8 in Europe. Amphimallon is a mostly Western Palaearctic genus of more than 60 species, 40 of which occur in Europe. Omaloplia is a Western Palaearctic genus of about 30 species, 20 of which occur from Europe. Serica is a large Holarctic genus with more than 160 Palaearctic species and about 110 in the Nearctic region but our UK representative is the only one to occur in Europe. Members of this subfamily are readily identified among our chafer fauna as follows:
-Tarsi with two unequal claws.
-Tarsi with a single claw or two equal claws.
-Claws lacking lateral teeth.
-Claws with a single lateral tooth.
-Tarsi with a single claw.
-Tarsi with two claws.
-Small species, 6-10mm. Apical spurs on hind tibiae widely separated.
-Larger species, 14-30mm. Apical spurs on hind tibiae close together.
-8-10mm. Uniformly pale brown.
-6.7mm. Forebody black, elytra reddish-brown with dark borders.
-Smaller species, 14-20mm. Antennal club with 3 segments.
-Larger species, 20-35mm. Antennal club with 4-7 segments.
-Elytra with sparse and long pubescence, about as long as that on the pronotum. Antennal club dimorphic; in males 2-3mm, in females about 1mm.
-Elytra with very sparse and shorter pubescence, about half as long as that on the pronotum. Antennal club dimorphic; in males about 1.5mm, in females about 1.2mm.
-Larger species, 30-35mm. Elytra dark brown mottled with patches of white scales.
-Smaller species, 20-30mm. Elytra pale brown with evenly distributed pale pubescence.
-Pygidium shorter in both sexes and constricted before the apex. Third antennomere in males with a forward-facing spur. Antennal club about 4mm in males, about 1.5mm in females. Length 22-27mm.
-Pygidium longer in both sexes and narrowest at the apex. Third antennomere in males without a spur. Antennal club about 3.5mm in males, about 1.5mm in females. Length 20-30mm.